After getting started you will want to...
Read the contribution checklist on the wiki.
Have a look through the master todo checklist.
Have a look through the list of bugs.
Triage a bug, File a bug, fix a bug, or implement something new.
The glibc mailing lists are hosted on sourceware.org:
libc-announce: The libc-anounce list is used to inform users and developers of upcoming releases and anouncements.
libc-alpha: The libc-alpha list is for the discussion of glibc development. Please do not ask for build help on this list.
libc-help: The libc-help list is intended for all glibc questions including build problems, C library usage, and more. No question about glibc is ever wrong on this list.
libc-locales: The libc-locales mailing list is used for discussing locale specific changes and patches to glibc.
libc-stable: The libc-stable mailing list is used to discuss changes backported to stable branches. The list also receives git commit traffic for stable release branches. Distribution developers can subscribe to the list to track backports and determine if their own distribution branches need to be rebased and or if the stable release branch they depend upon needs backports.
libc-testresults: The libc-testresults mailing list is intended to centrally collect the test results of developer builds.
glibc-cvs, and glibc-bugs: The glibc-cvs and glibc-bugs lists exist solely to receive automated messages from git and from Bugzilla, respectively. Please do not post to these lists.